class_docstr: Dictionary for BERT task. This extends MaskedLMDictionary by adding support
  for cls and sep symbols.
docstr: Helper to get index of cls symbol
docstr_tok: ["Helper","to","get","index","of","cls","symbol"]
code: def cls(self):
      """Helper to get index of cls symbol"""
      return self.cls_index
  
file_path: fairseq/fairseq/data/legacy/masked_lm_dictionary.py
imports: from fairseq.data import Dictionary
label_desc: Use image node_id 2 for calling the BertDictionary obj's underlying member method code with example usage: obj.cls() and returns: self